This invention relates to a liquid crystal display device which uses a polymer dispersion type liquid crystal or polymer network liquid crystal as a liquid crystal layer, which does not require a polarizing film, and a method of fabricating the same.
There has been an increasing development of various types of liquid crystal display devices (display panels) which are rendered thin and light with low power consumption. There has been recently a growing demand for a lighter and thinner display device a high demand for a low cost display device.
As a means for rendering the liquid crystal display device thin and light, it is conceived that a substrate to be used is made thin. Since a glass substrate is generally employed by a liquid crystal display device, it is a most efficient means to render the liquid crystal display device thin and light by rendering the glass substrate thin.
There has been an increasing development of reflection-type liquid crystal display devices to obtain an excellent display quality even in outdoors in fine weather. Since the reflection-type liquid crystal display device can effect a display utilizing an external light without using a backlight consuming much power, it has been fairly developed so as to realize a liquid crystal display device having less power consumption.
Reflection-type liquid crystal display devices are roughly divided into two types, a first type is a device utilizing a polarizing film and a second type is a device not using a polarizing film.
A main type of the second reflection-type liquid crystal display device not using the polarizing film comprises two types, namely, one type using a liquid crystal layer composed of a guest-host liquid crystal including a dye contained in a liquid crystal, and another type using a liquid crystal layer composed of a polymer dispersion type liquid crystal having liquid crystal dispersed in a polymer or a polymer network type liquid crystal having liquid crystal which is present in gaps between net-like polymers.
Since these two types of reflection-type liquid crystal display devices effect display while the liquid crystal layer per se is varied in a transparent state and an opaque state depending on the presence or absence of a voltage applied to the liquid crystal layer, a polarizing film is not needed, thereby effecting a bright display.
As far as low cost is concerned, an honest and steady endeavor such as the reduction of cost of a material, saving of a material to be used, or the like is carried out.
There is a liquid crystal material as a typical wasteful material to be used, and various proposals are made for saving the liquid crystal material. As an example, there is proposed a liquid crystal display device as disclosed in JP 58-37527, B.
The outline of this liquid crystal display device is explained with reference to FIG. 5. The liquid crystal display device is fabricated integrally in a configuration where a plurality of liquid crystal display devices are arranged in a row as shown in FIG. 5. Respective liquid crystal display devices 10 comprise two transparent glass substrates 1, 2 (they seem only one glass substrate because they are overlapped with each other), and these glass substrates 1, 2 are bonded to each other to form given gaps 4 by seals 3 provided on portions of respective liquid crystal display devices 10.
Pouring ports 5 are provided on each side 3a (lower side in FIG. 5) common to the seals 3 at the center thereof for pouring liquid crystal material into the gaps 4 between two glass substrates 1, 2. Barriers 6 formed of the same sealing member are provided on both ends of the respective sides 3a so as to join the seals 3 of adjoining liquid crystal display devices 10.
The barriers 6 serve to prevent the liquid crystal material from entering between the seals 3 of the adjoining liquid crystal display devices 10 when pouring the liquid crystal material into the gaps 4 of a plurality of liquid crystal display devices 10 which are integrally formed with one another.
Accordingly, since the liquid crystal material proceeds forward inside the gaps 4 surrounded by the seals 3 of the respective liquid crystal display devices 10 and the front surface of the respective sides 3a in which each pouring port 5 is provided, the liquid crystal material scarcely enters unwanted areas, thereby saving the liquid crystal material to the maximum.
Further, if only the configuration of the seals 3 is devised, the barriers 6 can be formed at the same time when the seals 3 are formed so that the liquid crystal material can be saved without adding an extra process when fabricating the liquid crystal display device, thereby greatly contributing to the low cost of the liquid crystal display device.
After pouring the liquid crystal material into the gaps 4 of the respective liquid crystal display devices 10, the pouring ports 5 of the seals 3 are sealed by a sealing agent, not shown, thereby forming liquid crystal layers which are sealed between two glass substrates 1, 2 of the respective liquid crystal display devices 10.
Finally, two glass substrates 1, 2 are cut along positions depicted by prescribed cut lines 18, thereby separating the liquid crystal display devices 10 from each other so as to complete individual liquid crystal display devices 10.
Since the reflection-type liquid crystal display device not using a polarizing film can effect a bright display, it has been fairly developed, and it mainly comprises a type using a guest-host liquid crystal as a liquid crystal layer and another type using a polymer dispersion type liquid crystal or a polymer network type liquid crystal as the liquid crystal layer.
For example, when a display device using a polymer dispersion type liquid crystal or a polymer network type liquid crystal is fabricated, as explained with reference to FIG. 5, a liquid crystal material formed of a mixture composed of a monomer and the liquid crystal material is poured into the gaps 4 formed by the seals 3 between two glass substrates 1, 2 and the gaps are sealed, then the entire surface of the display device is irradiated with ultraviolet rays to polymerize the monomer in the liquid crystal material, thereby forming a liquid crystal layer formed of a polymer dispersion type liquid crystal or a polymer network type liquid crystal.
Meanwhile, typical liquid crystal display devices have terminal areas 14 having terminals provided on an internal surface of at least one of two glass substrates 1, 2 outside the seals 3 for electrically connecting electrodes (not shown) formed on the confronted inner surfaces of two glass substrates 1, 2 to an external circuit, as shown in FIG. 6.
When the liquid crystal display devices 10 are separated from one another by cutting two glass substrates 1, 2, the two glass substrates 1, 2 need to be separated at different positions so as to expose the terminal areas 14.
That is, the first substrate 1 positioned at the upper side in FIG. 6 is cut along first prescribed cut lines 7, and the second substrate 2 positioned at the lower side in FIG. 6 is cut along second prescribed cut lines 8, 8 every two positions so that the second substrate 2 confronting the terminal areas 14 of the first substrate 1 is removed when the liquid crystal display devices 10 are separated from each other, thereby exposing the terminal areas 14.
However, since the barriers 6 are formed of the same material as the seals 3, the terminal areas 14 formed on an inner surface of the first substrate 1 and the inner surface of the second substrate 2 confronting the terminal areas 14 are bonded to each other by the barriers 6 formed of a sealing member, so that the barriers 6 need to be peeled off by a force exceeding a force for adhering or bonding the glass substrates 1, 2 when the glass substrates 1, 2 are cut.
Since the sealing member has a strong adhesive force inherently, the terminal areas 14 of the first substrate 1 or a portion confronting the second substrate 2 is frequently broken before the unwanted portions of the second substrate 2 are removed by cutting.
The liquid crystal display devices 10 having the broken terminal areas 14 are of course faulty goods, and in the case of the liquid crystal display devices 10 having broken portions confronting the terminal areas 14, the broken portion remains on the terminal areas 14, and hence the liquid crystal display devices 10 are also faulty goods.
If the thickness of each substrate is rendered thin for rendering the liquid crystal display device 10 thin and light, this tendency becomes conspicuous. If glass having a thickness of about 0.5 mm is employed by each substrate, it is found that all the liquid crystal display devices 10 substantially become faulty goods by the same reason.
There are the following problems in the liquid crystal display device using the polymer dispersion type liquid crystal or polymer network type liquid crystal.
That is, if the barriers 6 shown in FIG. 6 are not provided, when a liquid crystal material formed of a mixture composed of a liquid crystal and a monomer is poured into the gaps of the respective liquid crystal display devices 10, the liquid crystal material enters the gaps between the seals 3 owing to capillary phenomenon to be also stuck to the terminal areas 14. Thereafter, if the liquid crystal material is irradiated with ultraviolet rays as it is, the monomer in the liquid crystal material on the terminal areas 14 is reacted to be polymerized.
Accordingly, even after the liquid crystal display devices are separated into individual ones, the polymerized liquid crystal material remains stuck to the surfaces of the terminal areas 14.
Since the polymerized liquid crystal material has a high insulating property, electric connection to the external circuit on the terminal areas 14 becomes difficult. Accordingly, it was necessary to have a special device not to render the liquid crystal material stuck to the terminal areas 14 not to be irradiated with ultraviolet rays or to provide a special process to completely remove the polymerized liquid crystal material, which was however difficult to carry out.
The invention has been developed to solve the foregoing problems, and it is an object of the invention to provide a liquid crystal display device capable of preventing a liquid crystal material from entering unwanted portions to save the amount of use of a liquid crystal material, and preventing a liquid crystal material particularly formed of polymer dispersion type liquid crystal or polymer network type liquid crystal from sticking to terminal areas of substrates, and preventing the substrates from being broken when the substrates are cut to separate the liquid crystal display devices into individual ones, so that a fabricating yield is improved to a greater extent.
To achieve the above object, the invention provides a liquid crystal display device having the following construction and a method of fabricating the same.
The liquid crystal display device according to the invention comprises two transparent substrates, a seal for forming a gap between the two substrates by joining the two substrates, a liquid crystal layer formed of a polymer dispersion type liquid crystal or a polymer network type liquid crystal sealed in the gap and a pouring port provided in the seal for pouring a liquid crystal material to form the liquid crystal layer.
The liquid crystal display device is characterized in further comprising barriers provided in the vicinity of both ends of one side of the seal between the substrates where the pouring port is provided for preventing the liquid crystal material from turning around the pouring port when the liquid crystal material is poured from the pouring port into the gap between the two substrates, wherein an adhesive force between the barriers and at least one of the substrates is weaker than that between the seal and the substrate.
Further, in the case of the liquid crystal display device having terminal areas provided on an inner surface of at least one of the two substrates outside the seal and having terminals thereon for electrically connecting electrodes formed on the transparent substrate to an external circuit, the foregoing barriers are provided for preventing the liquid crystal material from turning around into the terminal areas when the liquid crystal material is poured from the pouring port into the gap between the two substrates.
The respective barriers may be formed of a conductive paste or the like having an adhesive force which is weaker than that of the seal.
Alternatively, the liquid crystal display device further includes an intermediate layer formed of a transparent organic material provided between the barriers and at least one of the two substrates, thereby weakening the adhesive force between the barriers and the substrate.
The liquid crystal display device according to the invention has the barriers for preventing the liquid crystal material from turning around to an outer periphery of the seal when pouring the liquid crystal material into the gap formed by the seal between the two substrates, thereby reducing a wasteful liquid crystal material to a greater extent. Further, a liquid crystal material is prevented from sticking to terminal areas of the substrate to form an insulating film when it is irradiated with ultraviolet rays, thereby preventing electric connection to an external circuit from being difficult.
Further, the barriers of the invention are different from the conventional barriers, namely, an adhesive force between the barriers and the substrate is weaker than an adhesive force between the seal and the substrate. Accordingly, when the liquid crystal display devices are separated from one another into individual ones after a plurality of liquid crystal display devices are formed on the same substrates, it is possible to prevent the fabrication of inferior or faulty liquid crystal display devices owing to the breakage of substrates, thereby improving a fabricating yield to a greater extent.
The method of fabricating a liquid crystal display device of the invention has the following steps.
(1) A step of forming a seal for sealing a liquid crystal layer on an inner surface of one of two transparent substrates having respectively electrodes on confronted inner surfaces thereof while leaving a pouring port for pouring a liquid crystal material;
(2) A step of forming connecting means provided outside the seal for electrically connecting the electrodes formed on the two substrates, and barriers for preventing the liquid crystal material from turning around into a portion where the connecting means are provided when the liquid crystal material is poured from the pouring port of the seal, respectively on an inner surface of one or the other of the two substrates wherein the connecting means and the barriers are respectively formed of a conductive material having an adhesive force weaker than that of the seal;
(3) A step of forming a gap between the two substrates by joining the two substrates via the seal;
(4) A step of pouring the liquid crystal material formed of a mixture composed of a liquid crystal and a monomer from the pouring port provided in the seal into the gap, then sealing the pouring port; and
(5) A step of forming the liquid crystal layer formed of a polymer dispersion type liquid crystal or polymer network type liquid crystal by irradiating the liquid crystal material with ultraviolet rays to polymerize the monomer.
The foregoing connecting means and barriers can be formed by printing using a conductive paste such as a silver paste or a carbon paste
The method of fabricating the liquid crystal display device of the invention may have the following steps of A to F.
A. a step of forming seals for respective liquid crystal display devices to seal liquid crystal layers on an inner surface of one of two transparent substrates while leaving pouring ports for pouring a liquid crystal material so as to fabricate a plurality of liquid crystal display devices at the same time,
B. a step of forming barriers in the vicinity of both ends of a side of each seal on an inner surface of one or the other of the two substrates where the pouring ports are provided for preventing the liquid crystal material from turning around to portions between the adjoining liquid crystal display devices when the liquid crystal material is poured from the pouring ports, wherein the barriers are formed of a material having an adhesive force weaker than that of the seals in the manner that the barriers between adjoining liquid crystal display devices are continuous with one another,
C. a step of forming gaps for use in respective liquid crystal display devices between the two substrates by joining the two substrates via the seals;
D. a step of pouring the liquid crystal material formed of a mixture composed of a liquid crystal and a monomer from the pouring ports provided in the seals into the gaps for respective liquid crystal display devices, then sealing the pouring ports;
E. a step of forming the liquid crystal layers made of a polymer dispersion type liquid crystal or polymer network type liquid crystal by irradiating the liquid crystal material sealed in the gaps with ultraviolet rays to polymerize the monomer; and
F. a step of cutting the two substrates along portions where the barriers are formed to separate the liquid crystal display devices from one another.
The connecting means and the barriers may be formed on an inner surface of one of or the other of the two substrates via intermediate layers respectively formed of a transparent organic material by changing the foregoing step of B.
Further, in the case of fabricating a liquid crystal display device provided with terminal areas on an inner surface of at least one of the substrates outside the seals, wherein the terminal areas have terminals for electrically connecting the electrodes provided on the substrates to an external device, the foregoing step of B may be changed to the following.
That is, there are formed the barriers for preventing the liquid crystal material from turning around into terminal areas respectively on an inner surface of one or the other of the two substrates when the liquid crystal material is poured from the pouring ports of the respective seals, wherein the barriers are formed of a material having an adhesive force weaker than that of the seals or they are formed via intermediate layers made of a transparent organic material in the manner that the barriers between adjoining liquid crystal display devices are continuous with one another, on an inner surface of one or the other of the two substrates.
In the foregoing step of B or in a step where the foregoing step of B is partially modified, the barriers may be formed by printing using a conductive paste such as a silver paste or a carbon paste. Further, when the barriers are formed via the intermediate layer formed of a transparent organic material, the barriers per se may be formed of the same material as the seals.